1. Field of the Invention
The present invention relates to semiconductor manufacturing processes that use chemicals to treat a wafer. In particular, the present invention is directed to a method and apparatus for automatically measuring the concentration of total organic carbon (TOC) in ultra-pure water and chemicals that are used in a semiconductor manufacturing process, e.g., a wet etch process.
2. Description of the Related Art
Throughout the entire semiconductor manufacturing process, ultra-pure water is used as a cleaning solution. The content of the ultra-pure water is strictly monitored and controlled because the wafer yield is influenced by the quality of the ultra-pure water. A main indicator of the water quality is total organic carbon (TOC) content, which is a representative characteristic of the quality of the ultra-pure water that is to be controlled.
Complex and various ultra-pure water producing processes, such as a process for removing organic elements contained in city water, and a process for sterilizing microbes, etc. are required to limit the amount of TOC in the ultra-pure water. The accumulation of microbes in ultra-pure water piping increases the concentration of the TOC in the ultra-pure water. High concentrations of TOC degrade the efficacy of the ultra-pure water or act to contaminate the wafers during their processing. Therefore, ultra-pure water is extracted from ultra-pure water pipes on demand and the pipes are regularly cleaned using hydrogen peroxide.
FIG. 1 shows a conventional semiconductor manufacturing system that monitors, in-line, the concentration of TOC in ultra-pure water fed to a process section 16. The process section 16 includes a plurality of baths 18 in which a wafer is treated. First through nth chemicals are supplied to respective ones of the baths 18 from first through Nth chemical supply sources 12 and 14. On the other hand, ultra-pure water used to clean the wafers after being treated with the chemicals is supplied from a pure water source 10 to a respective bath 18 via an ultra-pure water supply line 10a. An analyzer 20 capable of analyzing the ultra-pure water for its TOC content is disposed in the ultra-pure water supply line 10a. Information from the analyzer 20 is used to control the TOC to remain below a specific level.
Unfortunately, the conventional semiconductor manufacturing system suffers from several problems as follows:    (a) varying quality levels of ultra-pure water and chemicals are not monitored and managed substantially;    (b) production accidents resulting from a mis-injection of chemicals cannot be prevented; and    (c) an influence of a varied contamination level on yield or reliability cannot be perceived because states or degrees of contamination of wafers subjected to processes of one hundred or more are not checked.